FIG. 6 shows a motor driving system according to the conventional technology. This motor driving system has a controller 100 and a plurality of motor driving control units 110 each provided with respect to each motor 50. The controller 100 issues a control command or the like to each of the motor driving control units 110. The controller 100 has a CPU 101, and a communication interface 102 used for executing infrared communications with the motor driving control unit 110.
The motor driving control unit 110 is based on an inverter system. The motor driving control unit 110 comprises a rectifier circuit 111 formed with a rectifier diode and a smoothing capacitor, a regenerating circuit 112 formed with a regenerative resistor and a regenerative transistor, an inverter circuit 113 for inverting output from the rectifier circuit 111 to an AC voltage for motor driving, a current detector circuit 114, a CPU 115 for providing controls over the inversion and regeneration; and a communication interface 116 for executing infrared communications with the controller 100.
In the conventional motor driving system, the controller 100 and the motor driving control unit 110 incorporate infrared interfaces 102 and 116 respectively. The motor driving control unit 110 receives a command from the controller 100 in the form of infrared rays and controls the driving of the motor 50 based on this command. Thus, a communication cable is not required in this conventional system between the controller 100 and the motor driving control unit 110.
When a system is formed in such a way that a plurality of motor driving control units 110 are provided for one unit of controller 100 as shown in FIG. 6, an identification code is previously allocated to each of the motor driving control units 110, and the controller 100 appends an identification code to a command and sends the command only to a motor driving control unit 110 that is to be controlled. Further, when a plurality of motors 50 are operated in synchronism with each other by the motor driving control units 110, the controller 100 also issues a command to the corresponding motor driving control unit in order to control driving of each of the motor.
FIG. 7 shows a conventional motor driving control unit having an operating section 123. The motor driving control unit 110 comprises a rectifier circuit 117 formed with a rectifier for generating DC control power for driving the CPU 115 and a peripheral IC as well as with a smoothing capacitor, a switching power transistor 118, a control IC 119 for controlling the switching power transistor 118, an insulation-reinforced transformer 120 for insulating a primary-side potential from a secondary-side potential to generate a DC control source voltage for driving the CPU 115 and peripheral IC, a feedback circuit 121 for managing whether the DC control source voltage for driving the CPU 115 and peripheral IC is a regular voltage or not, an insulation circuit 122 with an insulation amplifier or the like used for insulating the primary-side potential which gives an electric shock to a person if touched from the secondary-side potential which does not give an electric shock to even if touched, and an operating section 123.
The internal circuits of this motor driving control unit 110 are divided into the primary-side potential which gives an electric shock to a person if touched and the secondary-side potential which does not give an electric shock even if touched. In FIG. 7, the portion above the dotted line is the primary-side potential and the portion below this dotted line is the secondary-side potential. The internal circuits corresponding to the primary-side potential are the rectifier circuit 111 for rectifying power to the motor driving control unit, regenerating circuit 112, inverter circuit 113, current detector circuit 114, rectifier circuit 117 for generating DC control power for driving the CPU 115 and peripheral IC, switching power transistor 118, and transistor control IC 119 or the like. The internal circuits corresponding to the secondary-side potential are the interface section 116, CPU 115 and peripheral IC section, operating section 123 such as a switch, and a display section.
The primary-side potential is insulated from the secondary-side potential by the insulation-reinforced transformer 120 which uses the feedback circuit 121 for managing a source voltage for driving the CPU 115 and peripheral IC, and the insulating circuit 122 using an insulating amplifier or the like.
In the motor driving control unit 110, the rectifier circuit 111 rectifies and smoothes AC or DC voltage as control power, and generates a DC voltage to input the voltage to the insulation-reinforced transformer 120. The DC voltage is outputted to the secondary side of the insulation-reinforced transformer 120 according to the winding ratio, and is used, in this case, for driving the CPU 115 and peripheral IC. The voltage is fed-back because precision is required in the voltage in the second side, therefore, the control IC 119 controls the power transistor 118 to be ON when the voltage is low, and the control IC 119 controls the transistor to be OFF when the voltage is high. As the control IC 119 is generally provided in the primary-side potential, a photocoupler is used inside the feedback circuit 121 in order to insulate the primary-side potential from the secondary-side potential. A voltage detection signal and a current detection signal in the primary-side potential are fetched to the CPU 115 in the secondary-side potential via the insulation circuit, while a regenerative drive signal and a IGBT drive signal are supplied from the CPU 115 in the secondary-side potential to a regenerative driving circuit and a IGBT driving circuit via the insulating circuit 122.
In the conventional motor driving system described above, when a number of motor driving control units provided with respect to one controller becomes larger, it may happen that the infrared rays from the controller may not reach to the motor driving control units due to the arrangement of the units. When the infrared rays do not reach a motor driving control unit, such a motor driving control unit will not operate as specified by a command, and there is a fear that the manufacturing line or the system may stop unintentionally.
Furthermore, in the conventional motor driving system, a distance to which the infrared rays can reach is limited. Therefore, it is necessary to place the controller with respect to a plurality of motor driving control units at such a position that the infrared rays from the controller will reach all the motor driving control units, so that there is a restriction over the placement of the units. Further, there is limitation over driving of the number of motors and over concurrent control of a large number of motor driving control units at a time, so that it has been difficult to perform a synchronized operation by a large-scale system or a large number of motors whose reliability and precision are required.
Further, in the conventional motor driving control unit, insulation-reinforced components such as a photocoupler, a transformer and an insulating amplifier are used for insulating a switch and a display unit or the like which are supposed to be touched by a person and a power source for driving a CPU and an IC from the primary-side potential which gives an electric shock to a person when touched. However, these components are costly, and in addition, an outer size of the unit becomes larger. Further, because the photocoupler has a limited life, the reliability may be affected when a large number of photocouplers are used.